The focus of this proposal is to study the mechanisms underlying inhibitory olfactory responses in mouse olfactory receptor neurons (ORNs). Specific aims are: (1) to determine whether Ca2+-activated Kplus channels mediate odor-induced inhibitory responses; (2) to determine if heptaldehyde elicits exclusively excitatory or inhibitory responses in ORNs of transgenic mice (POMP-I7-IRES-RFP) where odor receptor I7 is expressed in mature ORNs. Odor- induced inhibitory responses and their dependence on K+ and intracellular Ca2+ will be examined utilizing a combination of Ca2+ imaging and perforated patch-clamp recording. The transgenic mice will be generated by injection of a cDNA construct of POMP-I7-IRES-RFP into fertilized mouse oocytes. The proximal 0.9 Kb of the olfactory marker protein (OMP) promoter will drive expression of the mouse I7 odor receptor. An internal ribosomal entry site (IRES) will be used to create a bicistronic mRNA encoding for I7 odor receptor and red fluorescent protein (RFP; Clontech). Since I7 responds to heptaldehyde specifically, this will result in a mouse with a large percentage of neurons responding to a specific odor, heptaldehyde. This mouse will be used to more stringently study mechanisms involved in inhibitory responses and the interaction between excitatory and inhibitory pathways in the same cells. Results gained from this study will expand our knowledge of odor detection and olfactory coding.